Plastifiers, method of preparation and PVC compositions containing same

ABSTRACT

Block copolyesters and block copolyesterurethanes are presented which are useful as plastifiers for PVC. The plastifiers, depending on process variations, contain ordered or random blocks of amorphous and semi-crystalline structure and are characterized as being highly compatible and substantially non-fugitive when blended with PVC.

BACKGROUND OF THE INVENTION

A plasticizer is a material incorporated in a plastic to increase theworkability, flexibility or distensibility (elongation) of the plastic.Plasticization on the molecular level, according to theory, is theweakening or rupturing of selective "bonds" while leaving others strongto make possible the shaping, flexing or molding of the material beingplasticized.

Although natural plasticizers, e.g., water, camphor, oils, pitch, etc.,have been used since the earliest days of recorded history, it has onlybeen since the early 1900's that synthetic materials have been used toplasticize resins and polymers. Since the advent of polyvinyl chloride(PVC), the most generally used synthetic plasticizers have been theesters of phthalic and phosphorus acids, e.g., dioctyl phthalate,diphenyl phthalate, tricresyl phthalate, triphenyl phosphate and thelike. Monomeric plasticizers, while admirably fulfilling their functionof external plasticization of PVC, have lately come under increasingpressure from environmentalists since they are known to "bloom", i.e.,exude to the surface of a plasticized polymer and migrate to othermaterials in contact therewith. Despite the regulatory status and longsafe history of plasticizer usage, the migration of phthalates and otherplasticizers to medical and food products has caused considerableconcern and incentive to search for truly permanent external plasticizersystems.

Because of the shortcomings of conventional monomeric plasticizers,e.g., volatility, extractability and migration, a considerable amount ofresearch has been conducted in an effort to develop a truly permanent,high molecular weight polymeric modifier for PVC which is nonfugitive.The term "plastifier" has been coined to describe such modifiers todistinguish them from the conventional liquid to semi-solid typeexternal plasticizers, usually monomeric, heretofore used as modifiersfor PVC. The need is obvious for a plastifier which would have theproperties of high permanence in the plastified system and goodefficiency combined with a low order of toxicity and environmentalsafety.

SUMMARY OF THE INVENTION

It has now been found that copolyesters and copolyesterurethanes, havinga particular structural sequence of amorphous and semi-crystallineblocks and which are of a high molecular weight, may be used asplastifiers for PVC. Such plastifiers afford a high degree of permanencewith good efficiency, low toxicity and environmental stability. As willbe further described hereinafter, the plastifiers of this invention maybe prepared in random or ordered fashion to afford block copolyestersand block copolyesterurethanes useful as plastifiers for PVC.

PRIOR ART

Following is a description of the most pertinent prior art known toapplicant:

U.S. Pat. No. 2,691,006 describes linear ordered crystallinecopolyesters containing a plurality of polyester sequences, at least twoof which have an average sequence length of at least two ester units.The copolyesters are prepared by coupling separately prepared differentpolyesters. Thus, a hydroxy-terminated polyester and an acidchloride-terminated polyester are condensed or two separately preparedpolyesters having both hydroxy and carboxyl end groups may be coupledwith a diisocyanate or other coupling agent. In the preparation of thepolyesters, which may be coupled or condensed with each other, there areused aromatic or aliphatic dicarboxylic acids and glycols. There is noconcept disclosed which describes the combining of amorphous andcrystalline polyesters to obtain a high molecular weight copolyesterhaving particular sequences of amorphous and crystalline structure.

U.S. Pat. No. 3,446,778 describes the preparation of compositecopolymers characterized by a crystallizable predominantly aromaticpolyester block and an amorphous rubbery block. The crystalline andamorphous blocks are joined via a coupling agent. There is no concept ofsequentially coupling a polyester prepared from a diacid and anon-crystallizing glycol with a polyester prepared from a diacid and amixture of crystallizing and non-crystallizing glycols.

PREFERRED EMBODIMENTS OF THE INVENTION

In general, the plastifiers of the present invention are prepared bycoupling amorphous and semi-crystalline hydroxy-terminated polyesterprepolymers and extending the coupled prepolymers into a high molecularweight block copolymer. The resultant block copolymer is a blockcopolyester or block copolyesterurethane depending upon the agent usedto effect coupling of the prepolymer molecules. Thus, if the couplingagent is an acid halide, e.g., adipoyl chloride, the resultant highpolymer will be a copolyester. If the coupling agent contributesurethane linkages, the resultant high polymer will be a blockcopolyesterurethane.

By controlling the sequence of the addition of the reactants, a varietyof block copolymers, each having its own unique characteristics, may beobtained. The main varieties of block copolymers which are obtained inaccordance with this invention may be illustrated by three varieties ofblock copolymers which have been arbitrarily designated as (A) ordered,(B) ordered-random and (C) macrorandom. These main varieties of blockcopolymers are representationally described below. ##STR1##

In the above representations, the straight lines representsemi-crystalline blocks and the --X--X-- lines represent amorphousblocks. In the structure of the macrorandom copolymer, one or more endgroups may be semi-crystalline or amorphous. The dots represent ester orurethane links between molecules. In general, the copolymers of theinvention are comprised of amorphous end blocks constituting from about15 to about 50 percent by weight of the copolymer, based on the totalcopolymer, and a center block constituting, correspondingly, from about85 to about 50 percent of the copolymer.

The unique efficacy of block copolymers (A), (B) and (C) as PVCplastifiers is clearly demonstrated by comparison between them and anisomeric polymer of the same molecular weight which contains nosemi-crystalline/amorphous block units. Such a non-block copolymer isreferred to hereinafter as "microrandom" copolymer and data is presentedto show its non-utility as a PVC plastifier.

The polyester prepolymers which are used to prepare the high molecularweight plastifiers of the present invention are prepared by the reactionof aliphatic or aromatic dicarboxylic acids with aliphatic or aromaticdihydroxy compounds.

Exemplary dicarboxylic acids which are utilized in the process ofpreparing the prepolymers of the present invention are aliphatic andaromatic dicarboxylic acids having from about 4 to about 10 carbonatoms, e.g. succinic, glutaric, adipic, pimelic, suberic, azelaic,sebacic, phthalic and the like.

The dihydroxy compounds which are utilized in the preparation of theprepolymers used in the present invention are crystallizing andnon-crystallizing dihydroxy compounds. The crystallizing compounds areexemplified by ethylene glycol, 1,4-butylene glycol, 1,6-hexanediol,neopentyl glycol and the like. The non-crystallizing compounds areexemplified by 1,3-butylene glycol, 1,2-propylene glycol, 1,3-propyleneglycol, 2-ethyl-1,3-hexanediol, diethylene glycol, dipropylene glycoland the like.

The agents which are used to couple the prepolymers determine whetherthe polymer is a copolyester or a copolyesterurethane. Such agents areacid halides and isocyanates.

Acid halides which are used as coupling agents in accordance with thepresent invention include adipoyl chloride, oxalyl chloride, thephthaloyl chlorides, phosgene and the like.

Isocyanates which act as coupling agents in accordance with the presentinvention include hexamethylene diisocyanate, methylene bis-(p-phenylisocyanate), toluene diisocyanate, p-phenylene diisocyanate and thelike.

In the preparation of the polyester prepolymers, amorphous prepolymersare prepared by reacting a dicarboxylic acid as stated above, e.g.,adipic acid, with a non-crystallizing dihydroxy compound, e.g., adipicacid, with a non-crystallizing dihydroxy compound, e.g., 1,3-butyleneglycol. The semi-crystalline prepolymers are prepared by reacting adicarboxylic acid, e.g., adipic acid, and a mixture of dihydroxycompounds, one of which is non-crystallizing, e.g., 1,3-butylene glycol,and one of which is a crystallizing dihydroxy compound, e.g.,1,4-butylene glycol in a ratio of from about 0.1 to about 0.5,non-crystallizing to crystallizing dihydroxy compound.

As stated above, the preferred embodiments of block copolymers preparedin accordance with this invention are the ordered copolymer, theordered-random copolymer and the macrorandom copolymer.

The ordered block copolymer is prepared by initially making crystallineor semi-crystalline prepolymers and then coupling the prepolymers viaester or urethane links. Upon attainment of the crystalline orsemi-crystalline polymer of the desired molecular weight, separatelyprepared amorphous prepolymer and coupling agent are reacted with thecrystalline or semi-crystalline polymer chain. In such manner, thecopolymer comprises a center block which may be crystalline orsemi-crystalline and having amorphous end blocks. Accordingly, theordered copolymer has from about 20 to about 95 percent crystallinity,based on heat of fusion, as set forth below. The center block of theordered copolymer may, however, be from 20 to about 100 percentcrystalline depending on whether the prepolymer used in its preparationis semi-crystalline or crystalline. Preferably, the copolymer has acrystallinity of from about 20 to about 50 percent based on heat offusion. Especially preferred is a copolymer having about 30 percentcrystallinity. The ordered block copolymer has a molecular weight ofabout 85 to about 100,000 and has excellent compatibility with PVC.

The ordered-random copolymer is prepared by separately making amorphousand semi-crystalline prepolymers and then coupling them via ester orurethane links to form a block copolymer having randomly alternatingsemi-crystalline and amorphous blocks. Additional amorphous prepolymerand coupling agent are then added so that the randomly alternatingsemi-crystalline and amorphous block copolymer is capped with amorphousend groups. Accordingly, the ordered-random copolymer has from about 25to about 95 percent crystallinity based on heat of fusion. The center,semi-crystalline block may have from about 20 to about 95 percentcrystallinity, preferably from about 20 to about 50 percentcrystallinity. Preferably the copolymer has a crystallinity of fromabout 20 to about 50 percent based on heat of fusion. Especiallypreferred is a copolymer having about 25 percent crystallinity. Theordered-random block copolymer has a molecular weight of from about80,000 to about 100,000 and has excellent compatibility with PVC. Themacrorandom copolymer contains randomly alternating amorphous andsemi-crystalline blocks. Thus, it is prepared by separately preparingamorphous and semi-crystalline prepolymers of the desired molecularweight and then combining the prepolymers with a coupling agent andallowing random coupling to occur. The macrorandom copolymer has fromabout 20 to about 95 percent crystallinity, based on heat of fusion.Preferably, it has a crystallinity of from about 20 to about 40 percentcrystallinity. Especially preferred is a copolymer having about 30percent crystallinity. The macrorandom copolymer has a molecular weightof from about 85,000 to about 100,000 and has excellent compatibilitywith PVC.

The isomeric microrandom copolymer is so-named because the amorphous andcrystalline regions alternate on a molecular level rather than on aprepolymer level. Thus, it is prepared by reacting equivalent amounts ofthe dicarboxylic acid, non-crystallizing dihydroxy compound andcrystallizing dihydroxy compound to provide a prepolymer containingrandomly alternating molecules of crystallizing and non-crystallizingdihydroxy compound reacted with the dicarboxylic acid. This prepolymeris then reacted with a coupling agent to produce a high polymer. Thecharacteristics of the isomeric microrandom copolymer are a molecularweight of about 100,000 and poor compatibility with PVC.

The degree of crystallinity in the semi-crystalline prepolymers isdetermined by regulating the ratio of non-crystallizing dihydroxycompound to crystallizing dihydroxy compound and by delaying theaddition of the non-crystallizing dihydroxy compound. The degree ofcrystallinity in the block copolymers is governed by the ratio of theweights of crystalline or semi-crystalline and amorphous prepolymersused in the coupling reaction. Generally, the copolymers of theinvention have from about 20 to about 95 percent crystallinity, asdefined below.

A preferred copolyester or copolyesterurethane is the ordered-randomtype having a crystallinity of approximately thirty percent, based on acomparison of the heat of fusion of the copolymer under considerationwith the heat of fusion of poly(1,4-tetramethylene adipate) which is onehundred percent crystalline. The end blocks comprise about twentypercent of the copolyester or copolyesterurethane and the center blockcomprises about eighty percent of the copolyester or copolyesterurethaneand may contain about twenty percent amorphous segments by weight.

Regulation of the crystallinity is important when these copolymers areto be blended with another polymer, such as PVC. If crystallinity is toohigh, these copolymers will separate from the other polymer at thesurface, yielding an unsightly "bloom". If crystallinity is too low, asin the case of the microrandom copolymer, these copolymers take the formof tacky glasses, i.e. highly viscous liquids which are difficult tohandle, and which do not blend easily with other polymers, such as PVC.

Likewise, location of semi-crystalline segments is important, especiallywhen these copolymers are to be blended with another polymer. If thesemi-crystalline segments are at chain ends, these segments find iteasier to migrate to the surface and separate from the blend in the formof a solid "bloom".

In block copolymers prepared by coupling prepolymers, the prepolymersordinarily have a molecular weight (number average) of from about 1,000to about 10,000, preferably from about 2,000 to about 6,000.

The extended block copolymer (i.e., high polymer) ordinarily has amolecular weight of from about 50,000 to about 400,000, preferably fromabout 100,000 to about 200,000.

In preparing the polyester prepolymers, the ratio of dihydroxy compoundto dicarboxylic acid is generally from about 1.05 to about 1.50,preferably from about 1.10 to about 1.30.

In preparing the high polymer, the ratio of prepolymer to coupling agentis from about 10 to about 30, preferably from about 14 to about 18.

The following Examples are included herein by way of illustration andnot by way of limitation.

EXAMPLE 1

This example illustrates the preparation of an ordered blockcopolyesterurethane and an ordered block copolyester. The preparationsdiffer only in the coupling agent used.

(A) Preparation of Amorphous Prepolymer

To a stainless steel reactor, equipped with a heat source, an agitator,a refluxing fractionating column, condenser and vacuum system, therewere charged 0.47 mole adipic acid, 0.61 mole 1,3-butylene glycol and0.0003 mole titanium tetrachloride. Prior to charging the reactants, thereactor was filled with nitrogen. The reaction mixture was heatedrapidly to reflux and the reflux return to the fractionating column headwas adjusted to maintain reflux temperature of about 100° C. whileremoving water of esterification. The reaction mass was then heated toapproximately 200° C. and vacuum was applied to achieve distillation ofexcess glycol. The batch was held at approximately 200° C. for one hourand then cooled to room temperature. Xylene was added to the reactionmixture and the xylene solution was filtered and dried. The amorphousblock prepolymer was characterized by gel permeation chromatography,showing molecular weight of approximately 3,000, by hydroxyl content ofapproximately 0.36%, and by acidity level of approximately 0.2 meq/100g. The percent solids was 38%.

(B) Preparation of Semi-Crystalline Prepolymer

To the reactor described above, additionally equipped to allow chargingof 1,4-butylene glycol under vacuum, there were charged 0.48 mole adipicacid, 0.12 mole 1,3-butylene glycol and 0.38 mole 1,4-butylene glycoland 0.0003 mole titanium tetrachloride. A nitrogen atmosphere wasmaintained as described above. The batch was heated to approximately200° C. while removing water of esterification. After partial evacuationof the system, there was added 0.01 mole 1,4-butylene glycol, the batchwas heated to 215° C. and slow evacuation of the system was resumed.After excess glycol had distilled, the batch was cooled, vented to theatmosphere and dissolved in xylene. The warm batch was filtered anddried. The semi-crystalline block prepolymer was characterized by gelpermeation chromatography, showing molecular weight of approximately5,000, by hydroxyl content of approximately 0.54%, and by acidity levelof approximately 0.2 meq/100 g. The percent solids was 38%. The percentcrystallinity was 47%.

(C) Preparation of an Ordered Block Copolyesterurethane

To a stainless steel reactor equipped with a heat source, an agitatorand auxiliary charge tanks, there were charged 182 parts ofsemi-crystalline prepolymer solution described above and 25 parts ofxylene. The solution was heated to 140° C. and 7.8 parts ofhexamethylene diisocyanate in five approximately equal portions wereadded over a period of about 2 hours. Then, 98 parts of the amorphousprepolymer solution described above plus 120 parts of xylene were added.Next there were added 2.8 parts of hexamethylene diisocyanate in threeapproximately equal portions over a period of 1 hour. The reactionmixture was stirred at 140° C. for an additional hour, then 1 partabsolute ethanol was added after cooling the mixture to 80° C. Thepolymer was isolated by adding the reaction mass to a large excess ofcold methanol. The yield was 101 parts of polymer with a molecularweight of about 90,000. The 1,3-/1,4-butylene unit ratio was 0.46±0.01.

The corresponding copolyester was prepared in an analogous fashion,using adipoyl chloride/pyridine as the coupling agent.

EXAMPLE 2

This Example illustrates the preparation of an ordered-random blockcopolyesterurethane.

Steps (A) and (B) of Example 1 were repeated. Preparation of highpolymer was as follows:

(C) High Polymer

To a suitable vessel equipped with an agitator, heat source, refluxcondenser and water trap, there were charged 165 parts ofsemi-crystalline prepolymer solution and 41 parts amorphous prepolymersolution. The batch was heated to reflux and water was removed. To thebatch was added approximately 2.5 parts of hexamethylene diisocyanateand the entire mixture was heated to reflux until maximum viscosity wasreached. At that point, 53 parts of amorphous block prepolymer solutionand 0.9 parts hexamethylene diisocyanate was added and heating wascontinued until, again, maximum viscosity was reached. The batch wascooled to 75° C., dry ethanol was added and the copolyesterurethane wasprecipitated. The yield was 93 parts of polymer with a molecular weightof about 85,000, and a 1,3-/1,4-butylene unit ratio of 0.46±0.01.

EXAMPLE 3

This Example illustrates the preparation of a macrorandom blockcopolyesterurethane and a macrorandom block copolyester.

To a stainless steel reactor described above, there were charged 168parts of the semi-crystalline prepolymer solution described above and 97parts of the amorphous prepolymer solution described above. Xylene (100parts) was added and the solution was heated to 140° C. Over a period of4 hours 10.4 parts of hexamethylene diisocyanate was added in sixapproximately equal portions. The reaction mass was stirred at 140° C.for 2 hours, then cooled to 80° C. and 1 part of absolute ethanol wasadded. The polymer was isolated as described above and there wasobtained 105 parts of high polymer of molecular weight of about 95,000,and a 1,3-/1,4-butylene unit ratio of 0.46±0.01.

The corresponding copolyester was prepared in an analogous fashion usingadipoyl chloride/pyridine as the coupling agent.

EXAMPLE 4

This Example illustrates the preparation of the isomeric microrandomblock copolyesterurethane and microrandom block copolyester.

(A) Preparation of Microrandom Prepolymer

To a nitrogen purged stainless steel reactor, equipped with a heatsource, an agitator, a refluxing fractionating column, condenser andvacuum system there were charged 3.00 moles adipic acid, 2.22 moles1,3-butylene glycol, 1.67 moles 1,4-butylene glycol and 0.002 moletitanium tetrachloride. The reaction mixture was heated to refluxtemperature and the reflux return was adjusted to maintain refluxtemperature of about 100° C. while removing water of esterification. Thereaction mass was heated to about 200° C. and vacuum was applied toremove excess glycol. The batch was held at terminal conditions forabout one hour then cooled to 120° C. and sufficient xylene was added tomake a 38% solids solution.

The prepolymer had a molecular weight of about 4,000, a hydroxyl contentof about 0.40% and an acidity of about 0.2 meq/100 g. Its1,3-/1,4-butylene unit ratio was 0.46±0.01.

(B) Preparation of Microrandom Copolyesterurethane

To a stainless steel reactor as described in Example 2 there werecharged 500 parts of the solution of microrandom prepolymer describedabove. The reaction mass was heated to about 140° C. and 10.3 parts ofhexamethylene diisocyanate were added in three approximately equalportions over a 1 hour period. Then 80 parts of the prepolymer solutionwere added over a 4 hour period. After about an hour, 1 part of absoluteethanol was added.

The polymer was isolated by pouring the reaction mass into methanol anddecanting the supernatant liquid. The polymer had a molecular weight ofabout 80,000 and a 1,3-/1,4-butylene unit ratio of 0.46±0.01.

In like fashion the microrandom copolyester was made using adipoylchloride/pyridine as coupling agent.

The following Example illustrates the utility of the blockcopolyesterurethanes and block copolyesters as plastifiers for polyvinylchloride.

EXAMPLE 5

Polyesterurethanes of the ordered, ordered-random, macrorandom andmicrorandom types were prepared in accordance with Examples 1, 2, 3 and4, respectively. The ordered plastifier was a solid and was 29%crystalline. The ordered-random plastifier was a solid and was 27%crystalline. The macrorandom plastifier was a solid and was 32%crystalline. The microrandom polyesterurethane was a glass and was lessthan 10% crystalline.

Using standard technique, the four polyesterurethanes were blended intohomopolymeric polyvinyl chloride (GEON 102 EP F-5, B. F. Goodrich Co.)at a concentration of one part polyesterurethane per one part PVC. Thefour samples (100 parts PVC/100 parts polyesterurethane) were tested forfailure of the polyesterurethane characterized by haze (bloom) andexudation (humidity) and for water extraction of the polyesterurethane.The results of the tests are set forth below:

    ______________________________________                                        Polyesterurethane                                                                               Ordered- Macro-   Micro-                                               Ordered                                                                              Random   random   random                                    ______________________________________                                        Days to Humidity Fail                                                                      5-14     5-14     5-14   1                                          Shore A   72       72       72                                                T.sub.f  °C.                                                                     -25      -25      -25                                            Days to Bloom Fail                                                                         120      105      65     No data                                 % Loss to H.sub.2 O                   due to                                     50° (24 hr)                                                                      0.1      0.1      0.1    sample                                     80° (24 hr)                                                                      0.2      0.2      0.2    failure                                 ______________________________________                                    

The superiority of the polyesterurethanes of the present invention isobvious from the above data. Polyesters of the present invention wouldbe expected to exhibit similar superior characteristics.

Although polyvinyl chloride systems are illustrated in the Examples,similar results are obtained in other halogen-containing polymersystems, whether in the form of coatings, articles, foamed products,plastisols, organosols or the like.

The amount of plastifier added may be from about 1 to about 100 phr(parts per hundred parts resin).

Accordingly, the polymers which are plastified in accordance with thisinvention include vinyl halide polymers, i.e. simple, unmixedhomopolymeric vinyl chloride or copolymers or terpolymers in which thepolymeric structure of polyvinyl chloride is interspersed at intervalswith the residues of other ethylenically unsaturated compounds which areinterpolymerizable therewith. The essential properties of the polymericstructure of polyvinyl chloride are retained if not more than about 40percent of a comonomer is interpolymerized therewith. Suitablecomonomers include vinyl halides such as vinyl bromide or vinylfluoride; vinyl esters such as vinyl acetate, vinyl chloroacetate, vinylbutyrate and fatty acid vinyl esters; vinyl alkyl sulfonates;trichloroethylene; vinyl ethers such as vinyl ethyl ether, vinylisopropyl ether and vinyl chloroctyl ether; aromatic an cyclicunsaturated compounds such as styrene, the mono- and polychlorostyrenes,coumarone, indene, vinyl naphthalene, vinyl pyridine, vinyl pyrrole;acrylic acid and its derivatives such as ethyl acrylate, methylmethacrylate, ethyl methacrylate, ethyl chloroacrylate, acrylonitrileand methacrylonitrile; vinylidene compounds such as vinylidene chloride,vinylidene bromide; unsaturated hydrocarbons such as ethylene, propyleneand isobutenes; allylic compounds such as allyl acetate, allyl chlorideand allyl ethyl ether; conjugated and cross-conjugated ethylenicallyunsaturated compounds such as butadiene, isoprene, chloroprene,2,3-dimethylbutadiene-1,3, piperylene, divinyl ketone and esters such asdiethyl maleate and diethyl fumarate.

Specific interpolymers which may be flame retarded in accordance withthe present invention include vinyl chloride/vinyl acetate,ethylene/vinyl chloride/vinyl acetate, ethylene/vinylchloride/acrylonitrile and the like.

Similarly, other halogen-containing polymers contemplated herein includehalogenated olefins, e.g., chlorinated polyethylene and chlorinatedpolypropylene; halogenated diolefins, e.g., chloroprene; chlorinatedparaffins and chlorosulfonated polyolefins, e.g., chlorosulfonatedpolyethylene and the like as well as polyblends of suchhalogen-containing polymers with non-halogenated resins.

While the invention has been described by referring to certain specificembodiments, it is not so limited since many modifications are possiblein the light of the above teachings. The invention may therefore bepracticed otherwise than as specifically described without departingfrom the spirit and scope thereof.

What is claimed is:
 1. An ordered-random, solid, blockcopolyesterurethane having from about 15 to about 50 percent by weightamorphous end blocks and from about 85 to about 50 percent by weightrandom copolymer center block having from about 20 to about 95 percentcrystallinity based on heat of fusion, said copolyesterurethane havingfrom about 25 to about 50 percent crystallinity based on heat of fusion,said random copolymer having randomly alternating amorphous andsemi-crystalline prepolymer blocks coupled via ester or urethanelinkages, said semi-crystalline prepolymer being prepared by reactingdicarboxylic acid with a mixture of non-crystallizing dihydroxy compoundand crystallizing dihydroxy compound in a ratio of non-crystallizingdihydroxy compound to crystallizing dihydroxy compound from about 0.1 toabout 0.5, and said end blocks and center block beingisocyanate-coupled.
 2. Copolyesterurethane of claim 1 having acrystallinity of about 25 percent.
 3. Composition comprising ahalogen-containing polymer and a copolyesterurethane of claim
 1. 4.Composition of claim 3, said halogen-containing polymer being a vinylchloride polymer.
 5. Composition of claim 4, said end blocks beingprepared by reacting aliphatic dicarboxylic acid having from about 4 toabout 10 carbon atoms with dihydroxy compound selected from 1,3-butyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol,2-ethyl-1,3-hexanediol, diethylene glycol and dipropylene glycol. 6.Composition of claim 5, said non-crystallizing dihydroxy compound beingselected from 1,3-butylene glycol, 1,2-propylene glycol, 1,3-propyleneglycol, 2-ethyl-1,3-hexanediol, diethylene glycol and dipropyleneglycol, said crystallizing dihydroxy compound being selected fromethylene glycol, 1,4-butylene glycol, 1,6-hexanediol and neopentylglycol, and said acid being aliphatic dicarboxylic acid having fromabout 4 to about 10 carbon atoms.
 7. Composition of claim 6, said endblocks being prepared by reacting aliphatic dicarboxylic acid havingfrom about 4 to about 10 carbon atoms with dihydroxy compound selectedfrom 1,3-butylene glycol, 1,2-propylene glycol, 1,3-propylene glycol,2-ethyl-1,3-hexanediol, diethylene glycol and dipropylene glycol. 8.Composition of claim 7 wherein said dicarboxylic acid is adipic acid,said non-crystallizing dihydroxy compound is 1,3-butylene glycol andsaid crystallizing dihydroxy compound is 1,4-butylene glycol. 9.Composition of claim 8, said copolyesterurethane having a molecularweight from about 80,000 to about 100,000 and said end blocks and centerblock being hexamethylene diisocyanate-coupled.
 10. Copolyesterurethaneof claim 1, said end blocks being prepared by reacting aliphaticdicarboxylic acid having from about 4 to about 10 carbon atoms withdihydroxy compound selected from 1,3-butylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 2-ethyl-1,3-hexanediol, diethylene glycoland dipropylene glycol.
 11. Copolyesterurethane of claim 1, saidnon-crystallizing dihydroxy compound being selected from 1,3-butyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol,2-ethyl-1,3-hexanediol, diethylene glycol and dipropylene glycol, saidcrystallizing dihydroxy compound being selected from ethylene glycol,1,4-butylene glycol, 1,6-hexanediol and neopentyl glycol, and said acidbeing aliphatic dicarboxylic acid having from about 4 to about 10 carbonatoms.
 12. Copolyesterurethane of claim 11, said end blocks beingprepared by reacting aliphatic dicarboxylic acid having from about 4 toabout 10 carbon atoms with dihydroxy compound selected from 1,3-butyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol,2-ethyl-1,3-hexanediol, diethylene glycol and dipropylene glycol. 13.Copolyesterurethane of claim 12 wherein the acid used in preparation ofsaid semi-crystalline prepolymer is adipic acid, said non-crystallizingdihydroxy compound is 1,3-butylene glycol and said crystallizingdihydroxy compound is 1,4-butylene glycol.
 14. Copolyesterurethane ofclaim 13 having a molecular weight from about 80,000 to about 100,000.15. Copolyesterurethane of claim 13, said end blocks and center blockbeing hexamethylene diisocyanate-coupled.